With the advances in technology in recent years, many complex electronic devices have been designed and mass produced for consumption by the public. Typically, the manufacture of such an electronic device includes numerous processes, many of which are automated to increase the speed and accuracy of production.
One such automated process, typically performed by a screen printer, is the process by which a reflowable conductive paste, e.g., solder paste, is selectively applied to a printed circuit (pc) board prior to placement of components on the pc board. Conventionally, a conveyor belt shuttles the pc board first beneath a fixed camera, which records and transmits the position of the pc board to a computer, and then beneath a frame, which holds a stencil corresponding to the pc board. In response to reception of the positional information from the camera, the computer calculates alignment information, which is transmitted to a servo-motor coupled to the frame. The servo-motor thereafter makes adjustments in the x, y, and .phi. coordinates of the frame such that the stencil is properly aligned with the pc board. Subsequently, the properly aligned stencil is dropped into contact with the pc board, and a squeegee blade wipes across the stencil to push solder paste through openings in the stencil onto the pc board. At the completion of this process, the stencil is lifted from the pc board, which is conveyed from beneath the stencil by the conveyor belt.
As long as only one type of pc board, i.e., pc boards having a specific configuration, such as receiver boards, is processed, the use of such a conventional screen printer provides for the fast and accurate application of solder paste to each pc board. If, however, a second type of pc board, i.e., pc boards having a different configuration, is to be processed, a new stencil, Which corresponds to the second type of pc board, must be placed in the frame of the screen printer. Additionally, the computer must be reprogrammed with features of the second type of pc board so that the correct alignment information is transmitted to the servo-motor. Because this initializing process can be time consuming, all of one type of pc board are commonly processed at one time, subsequent to which all of another type of pc board are processed.
One solution to this problem is to place more than one screen printer on a manufacturing line that is to be used to process more than one type of pc board, wherein each type of pc board correspond to a different pc board configuration. In this manner, one screen printer is employed to process pc boards of a first type, e.g., decoder boards, while a second screen printer processes pc boards of a second type, e.g., receiver boards. This kind of set up, therefore, in which one screen printer processes each type of pc board, eliminates the step of initializing a screen printer each time a different type of pc board is processed. However, each type of pc board must still be processed separately to avoid the possibility of pc boards being routed to the incorrect screen printer. As a result, because only one screen printer is active at any given time, the capacity of the manufacturing line is greatly under-utilized. Furthermore, because each screen printer is usually very expensive to purchase, the cost of manufacturing the pc boards increases, resulting in a greater product cost.
Thus, what is needed is a low cost screen printer capable of randomly processing pc boards having different configuration. A method, in a single screen printer which holds at least two solder stencils at the same time, for selectively applying solder paste to printed circuit (pc) boards having different configurations, comprises the steps of receiving a pc board and determining a pc board configuration. The pc board is then aligned with a first stencil held by the single screen printer if the pc board is of a first configuration, and solder paste is selectively applied thereto. The pc board is aligned with a second stencil held by the single screen printer if the pc board is of a second configuration, and solder paste is selectively applied thereto.